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Study also finds that converting conventionally farmed land would not overly harm crop yields or require huge amounts of additional land to feed rising populations

Converting land from conventional agriculture to organic production could reduce greenhouse gas emissions, the run-off of excess nitrogen from fertilisers, and cut pesticide use. It would also, according to a new report, be feasible to convert large amounts of currently conventionally farmed land without catastrophic harm to crop yields and without needing huge amounts of new land.

The study, published in the journal Nature Communications, found that by combining organic production with an increasingly vegetarian diet, ways of cutting food waste, and a return to traditional methods of fixing nitrogen in the soil instead of using fertiliser, the world’s projected 2050 population of more than 9 billion could be fed without vastly increasing the current amount of land under agricultural production.

This is important, as converting other land such as forests, cerrado or peatlands to agricultural use would increase greenhouse gas emissions from the land. The authors found that an increase in organic farming would require big changes in farming systems, such as growing legumes to replenish nitrogen in the soil.

However, other scientists were cautious over endorsing the report’s findings, pointing out that the size of the world’s agricultural systems and their variability, as well as assumptions about future nutritional needs, made generalisations about converting to organic farming difficult to make.

Sir Colin Berry, emeritus professor of pathology at Queen Mary, University of London, said: “As for all models, assumptions have to be made and what weight you attach to which item can greatly change outcomes. The assumption that grassland areas will remain constant is a large one. The wastage issue is important but solutions, not addressed here, to post-harvest- pre-market losses will be difficult without fungicides for grains. Some populations could do with more protein to grow and develop normally, despite the models here requiring less animal protein.”

Les Firbank, professor of sustainable agriculture at Leeds University, said: “One of the question marks about organic farming is that it can’t feed the world. [This paper] concludes organic farming does require more land than conventional methods, but if we manage the demand for food by reducing waste and reducing the amount of crops grown as animal feed, organic farming can feed the world.”

He warned: “[These] models can only be viewed as a guide: there are many assumptions that may not turn out to be true and all these scenario exercises are restricted by limited knowledge [and] are fairly simplistic compared to real life, but realistic enough to help formulate policy. The core message is valuable and timely: we need to seriously consider how we manage the global demand for food.”

Even without converting to organic production, however, the US, India, China and Russia – four of the world’s biggest greenhouse gas emitters – could turn into some of the biggest absorbers of carbon, through better management of their agricultural land.

A separate new study shows that these countries have the greatest potential for the sequestration of carbon dioxide through changing the way soils are protected, through better farming methods that can also help to preserve declining soil fertility.

Scientists said the potential of using soil as a carbon sink was equivalent to taking between 215m and 400m cars off the road, even if only small changes are made, of a kind which should be achievable on all farms. The study, published on Tuesday in the Nature journal Scientific Reports, and conducted by experts from the Chinese Academy of Science, the Nature Conservancy NGO, and the International Centre for Tropical Agriculture, found that farming crops differently could make a big contribution to achieving the goals of the Paris agreement on climate change.

Today’s intensive agricultural methods, involving frequent tilling of soils and the excessive use of chemical fertilisers, could be replaced with the revival of older methods such as the increased use of manure, cover cropping, mulching and growing trees next to cropland. However, the role of land management in preventing dangerous levels of climate change has often been overlooked at the talks, where discussions over the burning of fossil fuels have dominated. This is partly because of the urgency of switching away from fossil fuels, and partly because land management is a diffuse and diverse problem spread across the globe from small farmers to agri-industrialists, whereas fossil fuel sources tend to be larger and more monolithic, such as coal-fired power plants.

The results will be presented to delegates at the UN COP23 climate talks in Bonn on Wednesday. Nations at the talks are discussing ways to increase the commitments on emissions reductions made alongside the Paris agreement, and which scientists say are currently inadequate to hold the world to no more than 2C of warming, the binding target under the landmark 2015 accord.